A sub-slice base[lo:hi] advanced its data pointer by lo (element
COUNT) instead of lo*esz (BYTES), so the base pointer was wrong for
any esz>1 element. Pointer arithmetic is membsz-unit per the rt
invariant (ref/hare/rt/ensure.ha:30); esz==1 (u8/str) is unchanged.
Four emission sites, fixed byte-identically across stages (rule 10):
- value path: cmd/w6c/cgen.c N_SLICE <-> cgenexpr.ww cgslice
- call-arg: cmd/w6c/cgen.c:4646 <-> cgenutil.ww pushargsrev
Scaling mirrors the cgindex idiom: esz from the type table (rule 13;
cstage bu->sub->size, wwstage elemsizeofc) gated to an N_IDENT base,
uniform IMULQ (no SHL special-case, no immediate form -- w6a is
reg-reg only). The live lo reg is the multiplicand so the one free
GP (DX value / BX arg) holds esz*lo; lo is preserved for len (hi-lo)
and cap (base_cap-lo, #20). The esz==1 path keeps the single ADDQ,
byte-identical to before (#75/#20/str unaffected). Non-ident bases
stay unscaled in both stages (wwstage has no tnode there), tracked
as a #76 residual alongside #74.
New 943_subslice_ptresz_run: table-driven, dual-driver (ww/ww_ww),
esz in {2,4,8} array+slice base, lo>0, let-form + call-arg form;
asserts s[0]==base[lo] & s[1]==base[lo+1]. Fails on every fixture
pre-fix on both stages, passes post-fix. Registered in Makefile
(TESTS + target) so test/run builds and runs it.
Hojun-Cho
ab9de65b8e